LeetCode 958. Check Completeness of a Binary Tree

Question

Given the root of a binary tree, determine if it is a complete binary tree.

In a complete binary tree, every level, except possibly the last, is completely filled, and all nodes in the last level are as far left as possible. It can have between 1 and 2h nodes inclusive at the last level h.

https://leetcode.com/problems/check-completeness-of-a-binary-tree/

• Solution1

class Solution {
    public boolean isCompleteTree(TreeNode root) {
        boolean end = false;
        Queue<TreeNode> queue = new LinkedList<>();
        queue.add(root);
        while(!queue.isEmpty()) {
            TreeNode cur = queue.poll();
            if(cur == null) end = true;
            else{
                if(end) return false;
                queue.add(cur.left);
                queue.add(cur.right);
            }
        }
        return true;
    }
}

Complexity:

Time complexity: O(n)

Space complexity: O(n)